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AD7606C System Gain Calibration

Category: Datasheet/Specs
Product Number: AD7606C


I try to understand the AD7606C System Gain Calibration, but I have problems. I want to know what's resolution of gain error in LSB i can correct with the CHx_GAIN registers.

There is no clear description given in the datasheet, and I can make no sense out of Figure 93. "System Gain Calibration, with and Without Calibration", which I am not able to reproduce. When I try to calculate this myself, I get totally different values.

The FAQ mentions an application note ("A.N. 2011") that should explain further details, but that is nowhere to be found.

- Can you please give the formulas (Error (LSB) vs. Rfilter & Error (% of FSR vs. Rfilter)) that were used to calculate Figure.93?
- Can you please share the mentioned application note?

It seems that each bit in CHx_GAIN can correct a gain error of 32 LSBs, but I want to be sure.


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  • Hi Lluis,

    With the article and the corrections given I can now calculate want i wanted to know. Thanks a lot.

    I would love to see the datasheet corrected, but knowing how it is... Shrug

    As a side note: I like the idea behind the System Calibration Features, and letting the user correct for the external resistor while compensating the internal input impedance is quite nifty. One or two more bits would have been nice, and basing the calibration on a even 1000 R resistor, but there may be trade-offs involved, so this is what was possible.

    Thanks again, also for your quick responses!



  • Hi rehfi,

    Thanks for the feedback and for reporting those errors, I will try to get those corrections in, but unfortunately the process takes some time. 

    What do you mean by " basing the calibration on a even 1000 R resistor". This is the minimum change on resistance that you can compensate for, if you look at the saw-shaped plots, the worst-case error is still quite good. Would you have expected finer resolution on the ch_gain register?

    Thanks again!


  • Hi Lluis,

    what I meant was that it would be nice when the steps I can compensate for would be 1000Ω, and not 1024Ω. I guess I have an idea where the "1024" come from, but 1k steps is what I can usually buy and what will be commonly used.

    For the fun of it I looked up if I can buy 1024Ω resistors at Digikey, and it turns out that I actually can (Y11211K02400T), but in a clunky package and it costs a fortune.

    But that's mostly nitpicking. And in the end 1000Ω vs 1024Ω doesn't really matter much.

    I would not expect a finer resolution on the ch_gain register (although it has free bits!), but I would not say "no" if I could compensate the gain error even further down to 8 or 4 LSB PFS and NFS Error. But, as said, there may be trade-off involved when implementing this and just may not be so easy. It is how it is.